Processing modern audio files to make them appear to have originated from historic technology, called antiquing, is the inverse of restoring old recordings. Simulating both global and local degradations of older technologies can be useful in such applications as testing restoration algorithms. A theoretical analysis of old recordings combined with numerous case studies results in a convincing imitation of historic phonograph and gramophone recordings. This work was motivated by a museum that wanted to show how audio technology has evolved over the last 150 years.

A carefully controlled independent double-blind test with 27 listeners compared the Dolby Digital AC-3 standard compression codec with newer bandwidth extended codecs, Advanced Audio Coding Plus HE-AAC and Dolby Digital Plus E-AC-3. Subjective tests of this kind require a listening space that is physically and acoustically appropriate for detecting auditory nuances, mostly conforming to the standards of ITU-R BS.1116-1. Out of a large library of samples, a subset was selected based on their ability to challenge compression codecs. On average, AC-3 sounded better than the other two codecs.

The sampling and interpolation of the sound field along a circle is studied, and an angular sampling theorem is presented. Application of these results can be found in the problem of interpolating coarsely sampled head-related transfer functions (HRTFs). The proposed method interpolates HRTFs in a sub-band domain. For the low temporal frequencies satisfying the sampling theorem, HRTFs can be interpolated very precisely. At higher frequencies, the angular interpolation is carried out in a complex temporal envelope domain to limit aliasing. Numerical simulations indicate that the proposed method performs better in a mean square error sense than conventional interpolation methods.

A new approach for measuring distortion provides a continuous distortion curve versus frequency, and the method is suitable for use with noise, music, and multitone stimuli. Distortion measures are derived from dual-channel analysis of the noncoherence between the stimulus and the response. The mathematics is based on Volterra theory, which is an extension of linear system theory but applied to nonlinear systems. Because the technique uses standard signal processing, the approach is simple, accurate, and repeatable.